The instant invention relates to a process and structure for destroying hazardous and toxic chemical wastes. In the context of the subject disclosure, the present invention shall be referred to as the Pyrolytic and Combustion Destruct System (PCDS).
Toxic chemical wastes in the environment represent one of the most serious problems facing society today the world over. Ever increasing quantities of these toxic residues have overburdened the receiving environment (air, water, and land) and in many cases it can no longer handle the increasing rate of industrial waste generation and disposal. Today, the greatest percentage of hazardous waste is managed by landfilling, however, current environmental laws strictly limit this method of hazardous waste management. Because of stringent controls placed on hazardous waste management, many industries have been and will continue to be forced to close or restrict operations.
The need for proper disposal and management of hazardous and toxic wastes is an accepted reality. Land disposal has resulted in contamination of rivers, streams, and aquifers. Incineration is an alternative disposal method for destroying organic wastes, however, there has heretofore been no system capable of destroying such waste at commercially practical volumes and without regard to the physical state of the waste. In sharp contrast, the present invention is a significant breakthrough in this field in that it disposes of a large variety of hazardous waste (gases, solids, and liquids) in large quantities, it generates a by-product which is recycled, and it is energy efficient.
Although a large variety of hazardous wastes can be destroyed by incineration, complete destruction of hazardous waste by the incineration processes of the prior art can be quite complex, with the combustion temperatures, dwell time, feed conditions, and the physical and chemical characteristics of the wastes varying widely. For example, in the case of dioxins, these substances may be bound to particulate matter so tightly that they pass undestroyed through typical incineration systems.
Most toxic organic chemicals can be completely destroyed at 1832 degrees F. with a residence time of two seconds. It is believed that polychlorinated biphenyls and dioxins require 2200 degrees F. and two seconds dwell time. However, many wastes are completely destroyed at lower temperatures and shorter dwell times.
By the subject invention, the destruction of these chemicals is accomplished by a combination of pyrolysis and oxidation reactions. Unlike prior waste removal systems, the PCDS provides a system for the destruction of hazardous and toxic organic substances by pyrolysis and/or combustion. As used herein, pyrolysis refers to a chemical change in a substance resulting from heat alone which involves the breaking of stable chemical bonds, often resulting in molecular rearrangement. Similarly, as used herein combustion refers to a chemical reaction which produces light and heat.
The PCDS accommodates solids, sludges, liquids, and/or gaseous organic wastes. If desired, the PCDS can also accommodate inorganic heavy metal wastes, such metals being entrapped in the glass when solidified. The heavy metals cannot be readily released to the environment through the glass and they are not collected in the ash since there is no ash associated with the system.
The PCDS utilizes state-of-the-art methodology similar to the process for the manufacture of glass whereby the finished product is initially in a molten state during the chemical reaction process, and then becomes a solid glass product at ambient temperatures of 2200 degrees F. Temperatures ranging from 2300 to 2900 degrees F. in the molten mass, with flame temperatures exceeding 3000 degrees F. and combustion gas in the 2700 degree F. range, are realized in the glass manufacturing process. The PCDS system has been designed to provide an overall method to handle a large variety of hazardous wastes regardless whether they are liquid, solid, sludge or gaseous. The purpose of the PCDS is not to make glass per se, but to use the molten mass as the media for destruction of the hazardous and toxic substances.
Among the advantages the system has over present hazardous waste removal systems are: (1) it is capable of handling several ton size quantities of waste per hour, (2) an average temperature of 2600 degrees fahrenheit can be achieved and maintained during the reaction process, (3) dwell time for solids and liquids in the molten mass is in hours rather than seconds, (4) gases are in the combustion chamber and regenerator for at least 8 seconds, (5) the PCDS is capable of handling inorganic as well as organix substances, (6) the products can be re-cycled as raw material, and (7) during an emergency shutdown, the destruct process is continued at high temperatures for at least four hours ensuring that hazardous wastes are not vented or otherwise released to the atmosphere.
A basic understanding of the glass making process is helpful in appreciating the subject invention. In this connection, glass is typically produced in a continuous tank wherein the molten glass is maintained at a constant level and raw materials are fed at a rate equal to that at which the finished product is withdrawn. A typical glass furnace consists of a charging chamber called a doghouse wherein raw materials are fed to a melting chamber, a refining chamber which receives heated molten glass from the melting chamber and holds it for a time to achieve a suitable working temperature for withdrawl of the glass as a molten mass, and a space above the molten glass called the combustion chamber which provides combustion space for the flame. Frequently, two regenerator checkers chambers and an exhaust stack each having secondary checkers chambers, and a flue are included to complete the major components of a glass furnace.
The basic raw materials for making glass are composed of three predominate oxides: silica dioxide (sand), sodium oxide or soda ash, and calcium oxide or lime. The composition of glass is often expressed in terms of these oxides. For example, a typical glass product may comprise approximately 75 percent sand, 17.5 percent soda ash, and 7.5 percent lime. The melting of glass is carried out at temperatures ranging from about 2370-2925 degrees F. The heat must be sufficiently intense to bring about the reactions between the ingredients of the raw materials and to dissolve the silica.
With regard to the interior of a typical glass furnace, a regenerative continuous bridge wall tank furnace is often used for the on-going process wherein the glass forms a pool in the heart of the furnace, across which the flames impinge directly upon the molten material and the raw materials.
Heat recovery is commonly utilized whereby heat of combustion is stored by absorbtion from the spent flame gases, and in a succeeding cycle of the operation this heat is used to raise the temperature of incoming combustion air. In such an arrangement, the furnace commonly operates in two cycles which may be understood by following the path of the gases of combustion. The flame gases, having spent their heat on the interior of the furnace, leave the combustion chamber at a temperature only slightly higher than that of the furnace walls and contents, that is about 2730-2920 degrees F. These gases pass through chambers stacked with open brickwork which are herein referred to as regenerators or checker chambers. The outgoing gases yield approximately half of their heat content to the checkers which reach temperatures ranging from about 2370 degrees F. at the top or furnace side to 1200 degrees F. at the bottom or the flue side. At regular intervals of about 20-30 minutes, or when the prescribed temperature rise has taken place in a regenerator, the flow of the air and the fuel gas is reversed. The air now rises through the hot regenerator, becoming preheated. At the top of the regenerator, air and combustion fuel are contacted in a furnace port and produce a flame, the intensity of which is increased by the preheating. Combustion gasses pass through the furnace to a furnace port on the other side of divider structure 24 and enter a duplicate set of regenerator checker chambers completing the second cycle of operations.
A glass furnace often includes a continuous bridge wall tank which is built in two chambers, a melting chamber and a refining chamber, separated by a bridge wall. The bridge wall is usually two-layered, with an air space therebetween for ventilation to cool the blocks and retard corrosion. A passage in the bridge wall called the throat located at or near the bottom of the bridge wall leads the glass from the melting chamber to the refining chamber. A typical melting chamber of a 90 ton per day furnace is 16 feet wide, 24 feet long to the bridge wall, and 3 feet deep. The width gives ample distance for flame travel and the length provides the necessary area under the flame. The tank may be built, for example, of rectangular refractory blocks 12 inches thick and laid close together without mortar or cement. Since the outer surfaces of the blocks are exposed to the air and are relatively cool, the glass cannot penetrate a significant distance between the joints of the blocks without becoming so cold and stiff that it cannot flow out.
The bottom blocks may be of any suitable size to make up the required area of the melting chamber and should preferably extend about 1 foot in each direction from the outside dimension of the melting tank. The bottom blocks may be laid on a series of iron rods, for example, about 3/4 inch in diameter and laid across 6 inch I-beams spaced 18 to 24 inches apart. These are preferably supported on girders of 10 or 12 inch I-beams running longitudinally and resting on brick piers rising from a basement beneath the tank. The basement, which is approximately 15 feet deep, is necessary to provide the required height for the regenerator chambers. The side walls of the chambers may be, for example, 42 inches high and built of refractory blocks 18 to 24 inches wide.
At the back or the charging end of the melting chamber, there is a vestibule known as the doghouse. The doghouse is covered and provides an area wherein the batch is sintered before becoming exposed to the full velocity of the flames. At the front end of the melting chamber there is an opening which may be about 24 inches wide and 12 inches high known as the throat. This is built into the bridge wall with the opening flush with the bottom of the tank. The temperature of the refining chamber is normally about 572 degrees F. lower than that of the melting chamber.
Above the surface of the molten glass in a glass furnace is a combustion chamber commonly referred to as a superstructure for the flame as well as the final covering or crown. The superstructure typically consists of refractory walls called breast walls rising about two feet above the top of the blocks and supporting a crown arch on skew blocks. The breast walls may be offset 12 inches to the outside and are supported on steel members carried on brackets on the vertical buckstays, which brace the entire structure together.
The I-beams carrying the bottom blocks may project about 2 feet on either side; and on their outer ends are bolted heavy angle irons called heel plates, to carry the bottom ends of the buckstays. The buckstays rise above the height of the crown and are fastened together at the tops by tie rods at least 11/2 inch in diameter, and thus carry the horizontal thrust of the crown arch. The tie rods are threaded and provided with nuts which can be adjusted to allow for expansion as the furnace is heated. The crown of the melting chamber is typically an arch with a radius equal to its span. In a 90 ton per day unit this radius could be about 26 feet.
A glass furnace typically includes air ports in the wall through which fire enters the combustion chamber from a checkers chamber. Gas and air meet in the port neck, several feet from the inside of the wall, so that combustion is well under way as the mixture enters the tank. Fuel is fed through nozzles over ports, under ports, or in the sides of the port necks, directed towards the combustion chamber.
These burner nozzles are directed toward the batch of glass and at an angle toward each other so that the streams of gas cut across the stream of air, meeting in front of the port area.
Regenerator checkers chambers often are located behind the charging end of the melting compartment. In the unit described above, these chambers may have dimensions of about 8 feet wide, 14 feet long, and 12 feet high. The chambers are partitioned by a wall of fire and brick. The flues of exhaust stacks are spanned by rider arches to carry the firebrick checkers. The flues are frequently connected to two secondary checkers chambers. These secondary checkers are connected at one end to the stack for releasing the inert gases generated via the detoxication process to the atmosphere, and at the other end to a respective primary checkers chamber.
In addition, between the bridge wall and between the blocks and the buckstays, jack bolts, adjustable by turnbuckles, retain the block walls in position against the thermal expansion of the refractories and against the pressure of the molten glass. A system of wind pipes and nozzles for cooling the outside of the melting chamber walls and the melt line is generally required to retard corrosion.